Turner Enterprises spokesman Phillip Evans in Atlanta said the CNN founder was in hospital in South America and that "no further details will be provided".

CNN's news desk, however, tweeted that Turner was "under observation" in a hospital in Buenos Aires.

A security guard at the Instituto Argentino de Diagnostico y Tratamiento confirmed to the Associated Press that Turner was being treated there, but added that the institute's director told him that Turner's companions had asked for no information about his condition to be released.

The 75-year-old billionaire was first treated at the San Carlos Sanatorium in Bariloche, near his ranch in Argentina's Patagonia region. A spokeswoman there told the AP that Turner left that clinic after about four hours.

Turner owns 14 ranches in the United States and three in Argentina, including La Primavera, an 11,000-acre ranch along the Traful river in Argentina's Nahuel Huapi National Park.

The ranch hosts private expeditions and boasts some of the world's best trout fishing and hunting. Wild animals include deer, boar, quail, mountain lions and birds.

Some of his neighbours complained that they have been prevented them from accessing the river as it runs through his property, a claim his local management denied.